Recombinants between reovirus type 3 and 1 or 2 have been isolated. These will be used in studies on in vivo virulence; mapping of extragenic suppressor mutations; studies on the mechanism of reassortment. BIBLIOGRAPHIC REFERNCES: Cross, R.K. and Fields, B.N. Reovirus-Specific Polypeptides: analysis using discontinuous gel electrophoresis. J. Virol. 19: 62-173. 1976. Ramig, R.F., White, R.M. and Fields, B.N. Phenotypic suppression of a temperature-sensitive mutant of reovirus type III. Science 195:406-407, 1977.